Polymerization process

ABSTRACT

A process and catalyst for polymerizing 1-olefins, for example ethylene, the process comprising (a) supporting a chromium compound on a refractory oxide support material, (b) adding one or more tetravalent titanium compounds, (c) heating the product under such conditions that an active polymerization catalyst is formed, (d) and contacting the monomer with the active polymerization catalyst in the presence of (6) one or more organometallic compounds having wherein the metal is of groups 1A, 2A, 2B and 3A of the Periodic Table (Mendeleef), and (7) a polyene modifier. The refractory oxide support material is preferably silica and the titanium compound is preferably a tetraalkyl titanate. The organometallic compound can be, for example, a triakyl aluminium and the polyene can be for example a conjugated or unconjugated diene.

This is a continuation of application Ser. No. 133,825, filed Mar. 25,1980 abandoned.

The present invention relates to a process for polymerising 1-olefinsand to a catalyst therefor.

More particularly the invention relates to a process for polymerising1-olefins, for example ethylene, using a modified Phillips catalyst.Phillips catalysts have been extensively described in the literature.They are formed by supporting chromium trioxide, or a compoundcalcinable thereto, on a refractory oxide support material, for examplesilica, alumina, zirconia, thoria or silica-alumina and heating in anon-reducing atmosphere, preferably an oxidising atmosphere to producean active polymerisation catalyst. The produced catalyst is used topolymerise 1-olefins using the so-called "solution form" or "particleform" process. In the "solution form" process the monomeric 1-olefinwhich is normally ethylene or a mixture of ethylene with up to about 40wt % of other 1-olefins, is contacted with a suspension of the catalystin a liquid hydrocarbon which is a solvent for the polymer at thepolymerisation temperature employed. In the "particle form" process themonomer 1-olefin is contacted with a suspension or a fluidised bed ofthe catalyst particles in a fluid medium under conditions such that thepolymeric 1-olefin forms as solid particles suspended in or fluidised inthe fluid medium. The fluid medium can be for example a liquidhydrocarbon or a gas. Examples of suitable liquid hydrocarbons areisobutane and n-pentane. Examples of suitable gases are nitrogen orargon mixed with the gaseous monomer, or the undiluted gaseous monomer.Processes of this type are described in, for example UK patentspecifications Nos. 790,195, 704,641, 853,414, 886,784 and 899,156. Itis also known to modify Phillips catalysts with titanium compound, forexample to render the catalyst capable of producing polyolefins havingincreased melt index (i.e. lower molecular weight) or to increase thestress crack resistance of the produced polyolefin. Catalysts of thistype are described in, for example, U.S. Pat. No. 3,622,521 and UKpatent specifications Nos. 1,334,662 and 1,326,167.

U.S. Pat. No. 3,351,623 discloses a catalyst for polymerising ethyleneat a temperature in the range 275° to 335° F., i.e. under solution formprocess conditions, the catalyst being one which forms on mixing (1) anoxide component selected from the group consisting of silica; mixturesof silica and alumina containing up to 25 wt % alumina; and mixtures ofchromium oxide and at least one material selected from the groupconsisting of silica, alumina, zirconia and thoria, at least part of thechromium being in the hexavalent state at the initial contacting of themonomer therewith, (2) an organo metal component of formula R_(x) Mwherein R is selected from the group consisting of hydrogen and alkyl,aryl, cycloalkyl, alkoxy radicals and combinations of these radicalscontaining up to 12 carbon atoms, at least one R group being ahydrocarbon radical; M is selected from the group consisting ofaluminium, gallium, indium, thallium, zinc, boron, lead, lithium,zirconium, cabalt, magnesium and tin; and x is an integer equal to thevalence of M, and (3) a vanadium component selected from the groupconsisting of vanadium chelates and vanadyl chelates. U.S. Pat. No.3,351,623 seeks to produce a catalyst that permits the use of highpolymerisation temperatures to obtain relatively low melt index polymer.

Whilst the conventional particle form polymerisation process producespolyolefins suitable for many applications, there is a need for gradesof polyolefins having a high average molecular weight and broadmolecular weight distribution.

It is an object of the present invention to provide a process forpolymerising certain 1-olefins to polymers having increased averagemolecular weight and broader molecular weight distribution compared withconventional Phillips processes employing unmodified Phillips catalysts.

Accordingly the present invention provides a process for polymerisingethylene or a mixture of ethylene with up to 40 wt % (based on totalmonomer) of other 1-olefinic monomer comprising (a) supporting chromiumoxide, or a compound calcinable thereto, on a refractory oxide supportmaterial, (b) adding one or more tetravalent titanium compounds selectedfrom (1) TiO₂, (2) TiOCl₂, (3) titanium acetyl acetonate compounds, (4)alkanolamine titanates and (5) compounds having the general formulaTi(OR)_(m) X_(n), wherein m+n is 4, m is zero or an integer from 1 to 4,R is an organic hydrocarbon group having 1 to 12 carbon atoms, X ishalogen or a hydrocarbon group and when the titanium compound containsmore than one R or X group the groups may be the same or different, (c)heating the product under such conditions that an active polymerisationcatalyst is formed, (d) and contacting the monomer with the activepolymerisation catalyst in the presence of one or more organometalliccompounds having the general formula MR² _(p) Y_(q-p) wherein M is ametal of groups 1A, 2A, 2B or 3A or the Periodic Table (Mendeleef), R²is a hydrocarbon group containing 1 to 10 carbon atoms, Y is hydrogen orhalogen, q is the valency of M, p is an integer from 1 to q inclusiveand when the organometallic compound contains more than one R² or Ygroup they may be the same or different.

The monomer employed in the present invention is either ethylene or amixture of ethylene with up to 40 wt % preferably up to 25 wt % of other1-olefinic monomer, preferably 1-butene, 1-pentene, 1-hexene, or4-methyl-1-pentene.

The chromium compound can be chromium oxide (i.e. CrO₃) or a compoundcalcinable thereto, for example chromium nitrate, chromium carbonate,chromium acetate, ammonium chromate, chromyl chloride or tertiary butylchromate.

The refractory oxide support material can be, for example silica,silica-alumina, silica-titania, alumina, zirconia or thoria. Silica ispreferred, particularly silica having a mean particle diameter in therange 20 to 150 microns; and a surface area in the range 150 to 600square meters per gramme.

The quantity of chromium compound supported on the refractory oxide issuitably such as to provide a chromium concentration of at least 0.1%,preferably in the range 0.2-30 wt % most preferably 0.3-5.0 wt % basedon chromium compound and support together.

The supporting of the chromium compound on the refractory oxide supportmaterial can be achieved, for example, by dissolving a soluble chromiumcompound in a volatile liquid, impregnating the support material withthe solution and evaporating the solvent; by impregnating the supportwith a liquid chromium compound, e.g. chromyl chloride; by passing thevapour of a volatile chromium compound, e.g. chromyl chloride, into abed of the support material; or by mixing together a finely dividedchromium compound and the support material in the presence of a smallquantity of solvent, the quantity being insufficient to causesubstantial agglomeration of the support material, continuing the mixinguntil a substantially homogeneous mix is obtained and then evaporatingthe solvent. Examples of solutions that can be used to impregnate thesupport material are chromium trioxide/water, ammonium chromate/water,chromium acetate/water, tertiary butyl chromate/hexane, chromylchloride/chloroform.

When the titanium compound employed in the present invention isTi(OR)_(m) X_(n), R is preferably selected from alkyl, aryl, cycloalkyland combinations thereof, for example aralkyl and alkaryl, each grouphaving from 1 to 12 carbon atoms and X is preferably selected from R,cyclopentadienyl, alkenyl and halogen.

Titanium compounds represented by the formula (RO)₄ Ti are preferredparticularly the alkyl compounds having from 1 to 6 carbon atoms in eachalkyl group for example tetraethyl titanate and tetraisopropyl titanate.The titanium acetyl acetonate compound can be, for example, titaniumdiacetylacetonate di-isopropylate, titanium dichloro diacetyl acetonateor the so called "titanium acetyl acetonate" or "titanyl acetylacetonate". The alkanolamine titanate can be for example triethanolaminetitanate.

The quantity of titanium compound employed is suitably sufficient togive a titanium concentration in the product from step (b) in the range0.05 to 20 wt %, preferably 0.5 to 5 wt %.

The titanium compound is preferably added to the supported chromiumcompound in a form in which it becomes well dispersed. For example ifthe titanium compound is liquid it can be mixed with the supportedchromium compound as such, if desired. If it is a liquid or a solid itcan be dissolved in a suitable non-aqueous solvent or comminuted in anon-aqueous diluent and then mixed with the supported chromium compound.Alternatively, the titanium compound can be added as a vapour if it isvolatile, or carried into the supported chromium compound as an aerosolin a suitable carrier gas, for example nitrogen.

Further details of methods of adding titanium to Phillips-type chromiumoxide catalysts are described in UK patent specifications Nos.1,334,662, 1,326,167 and U.S. Pat. No. 3,622,521.

After the desired quantity of titanium compound has been added, theproduct is heated under conditions such that it is converted into amaterial catalytically active in polymerising 1-olefinic monomer. Thetemperature to which the supported chromium compound modified withtitanium must be heated to form an active polymerisation catalyst(hereinafter referred to as the activation temperature) is at least 250°C. and not higher than the temperature at which the support commences tosinter. Preferably the activation temperature is in the range 400° to900° C., most preferably 500° to 800° C. In general, the higher theactivation temperature employed within the aforementioned ranges, thelower becomes the average molecular weight of polyolefin produced overthe catalyst. The heating time is suitably within the range 5 minutes to24 hours, preferably 30 minutes to 15 hours although times outside thebroader range can be employed if desired.

It was formerly believed that to be an effective polymerisation catalysta "Phillips" catalyst must contain at least some chromium in hexavalentform. Whilst it is true that most, if not all, "Phillips" catalysts docontain hexavalent chromium it is now believed that the olefinpolymerisation catalysis may operate through chromium in valency statesbelow 6. Nevertheless it is desirable during the heat activation ofcatalysts of this type, including the catalyst employed in the processof the present invention, that conditions which favour the formation of,or retention of, chromium in the higher valency states should beemployed. The heat activation is preferably carried out in anon-reducing atmosphere and most preferably in an oxidising atmosphereor in vacuo. Dry air is an example of a suitable oxidising atmosphere.The heat activation must be performed under anhydrous or dehydratingconditions and the activated catalyst must be protected from ingress ofmoisture.

In the organometallic compound employed in the present invention the R₂group is preferably an alkyl, cycloalkyl or aryl group. Metal alkyls arepreferred, particularly aluminium trialkyls.

The metal present in the organometallic compound in the present ispreferably lithium, sodium, beryllium, magnesium, calcium, zinc cadmium,boron, aluminium or gallium. Metal alkyls particularly preferred aredibutyl magnesium, triethyl boron, triethyl aluminium, triisobutylaluminium. The quantity of organometallic compound employed is suitably0.1 to 100%, preferably 1 to 10 wt % based on the total weight ofcatalyst.

The polymerisation conditions employed in the present invention can beany of the conditions used in Phillips polymerisation processes.Preferably the polymerisation conditions are the so called "particleform" process conditions. In the "particle form" process the monomeric1-olefin is contacted with a suspension or a fluidised bed of thecatalyst particles in a fluid medium under conditions such that thepolymeric 1-olefin forms as solid particles suspended in or fluidised inthe fluid medium.

The fluid medium employed in particle form process conditions can be aliquid or a gas. Preferably it is a liquid. Examples of suitable liquidmedia are hydrocarbons which are chemically inert and non-deleterious tothe modified catalyst under the reaction conditions. Preferred liquidmedia are paraffins or cycloparaffins having from 3-30 carbon atoms permolecule, for example isopentane, isobutane, cyclohexane. Mostpreferably the liquid medium is isobutane.

When a liquid medium is employed in the process of the present inventionpreferably the concentration of monomer therein is in the range 2-20 wt% although concentrations outside this range can be employed if desired.

When the process of the present invention is under particle form processconditions the polymerisation temperature is preferably in the range 50°to 112° C., most preferably 80° to 108° C.

The polymerisation pressure is preferably in the range 2 to 100 bar whenthe fluid medium is a liquid and 1 to 60 bar when the fluid medium is agas. The residence or reaction time can vary from a few minutes toseveral hours and is generally in the range 15 minutes to 3 hours. Theparticle form process can be conducted under batch or continuouspolymerisation conditions. Preferably the conditions are continuous.Preferred apparatus for conducting the reaction under continuousconditions in a liquid medium is described in UK Patent SpecificationNo. 899,156.

For further details of examples of solution form and particle formprocess conditions and apparatus which can suitably be employed in theprocess of the present invention, reference may be made to UK PatentSpecification Nos: 790,195, 804,641, 899,156, 886,784 and 853,414.

The present invention further provides a catalyst for polymerising1-olefins prepared by (a) supporting chromium oxide, or a compoundcalcinable thereto, on a refractory oxide support material, (b) addingone or more tetravalent titanium compounds selected from (1) TiO₂, (2)TiOCl₂, (3) titanium acetyl acetonate compounds, (4) alkanolaminetitanates and (5) compounds having the general formula Ti(OR)_(m) X_(n),wherein m+n is 4, m is zero or an integer from 1 to 4, R is an organichydrocarbon group having 1 to 12 carbon atoms, X is halogen or ahydrocarbon group and when the titanium compound contains more than oneR or X group the groups may be the same or different, (c) heating theproduct under such conditions that an active polymerisation catalyst isformed, (d) and adding to the active polymerisation catalyst one or moreorganometallic compounds having the general formula MR² _(p) Y_(q-p)wherein M is a metal of groups 1A, 2A, 2B or 3A or the Periodic Table(Mendeleef), R² is a hydrocarbon group containing 1 to 10 carbon atoms,Y is hydrogen or halogen, q is the valency of M, p is an integer from 1to q inclusive and when the organometallic compound contains more thanone R² or Y group they may be the same or different.

The catalyst components and the methods of preparation are preferablysubstantially as hereinbefore described.

Isolation of the produced polymer may be conducted using the techniqueswell known in the art.

The invention is illustrated in the following Examples.

EXAMPLE 1 (a) Catalyst Preparation

30 g of a commercial chromia on silica catalyst base (ID 969, W R Graceand Co) was slurried in 300 ml petroleum ether (40°-60°), 4.5 g (4.7 ml)titanium tetraisopropylate (Titanium Intermediates Ltd) was added andthe petroleum ether distilled off in a rotary evaporator. The catalystwas stored under dry nitrogen, then activated by heating at 500° C. for5 hours in a bed fluidised with 900 ml/min of dry air. After cooling,the catalyst was stored under dry nitrogen. Analysis showed that itcontained 1.00% by weight Cr, 2.42% by weight Ti and 0.87% by weightCr^(VI).

(b) Polymerisation

Polymerisation was carried out in a 2.3 liter stainless steel stirredautoclave. The reactor was purged with nitrogen, baked out for 2 hoursat 110° C., then cooled to 102° C. The catalyst prepared as describedabove was charged to the reactor followed by 0.20 ml of a 10% by weightsolution of triethyl aluminum in n-hexane (=17 mg triethyl aluminium) inone liter of dry isobutane.

The reactor temperature was maintained at 102° C. and ethylene was addedto bring the total pressure in the reactor to 41.4 bar. Ethylene wasadded continuously throughout the run to maintain this pressure.Polymerisation and polymer property data are shown in Table 1. The Kdvalue is determined by a method similar to that given in Sabia, R, JAppl Polymer Sic. 1963, 7, 347. Kd is a measure of polymer shearresponse and, generally, Kd increases with breadth of polymer molecularweight distribution. The MI₂.16 is the `melt index` and the MI₂₁.6 the`high load melt index` determined according to ASTM method 1238 using2.16 kg and 21.6 kg loads respectively. The units are grammes per 10minutes. The melt index ratio MIR is MI₂₁.6 /MI₂.16.

EXAMPLE 2 (a) Catalyst Preparation

The method of preparation was the same as that used for Example 1, part(a) except that 50 g of ID969 catalyst and 3.1 ml of titaniumtetraisopropylate were used and the activation temperature was 600° C.Analysis of the catalyst showed that it contained 1.09% by weight Cr,0.80% by weight Ti and 1.02% by weight Cr^(VI).

(b) Polymerisation

The polymerisation was carried out as described in Example 1, part (b),except the polymerisation temperature in this case was 104° C.

The polymer data shown in the Table indicate that polymer of broadermolecular weight distribution has been prepared over the Phillipscatalyst modified with titanium and alkyl than would be made over anunmodified Phillips catalyst under the same polymerisation conditions.

                                      TABLE 1                                     __________________________________________________________________________    Example                                                                            Weight (mg)                                                                            Polymerisation                                                                        Yield (g)                                                                           Polymer                                           No.  Catalyst                                                                           AlEt.sub.3                                                                        Time (min).                                                                           of polymer                                                                          MI.sub.2.16                                                                       MI.sub.21.6                                                                       MIR Kd                                    __________________________________________________________________________    1    390  17  31      430   0.05                                                                              5.0 100 6.1                                   2    399  17  29      442   0.19                                                                              13.0                                                                              65.6                                                                              5.0                                   __________________________________________________________________________

I claim:
 1. A process for polymerizing ethylene or a mixture of ethylenewith up to 40 wt % (based on a total monomer) of other 1-olefinicmonomer comprising (a) supporting chromium oxide, or a compoundcalcinable thereto, at the heating temperature stated in part (c)hereof, on the refractory oxide support material comprising silica, (b)adding a tetravalent titanium compound having the formula Ti(OR)_(m)X_(n), wherein m+n is 4, m is zero or an integer from 1 to 4, R is anorganic hydrocarbon group having 1 to 12 carbon atoms, X is halogen or ahydrocarbon group and when the compound contains more than one R or Xgroup, the groups may be the same or different, (c) heating the productat a temperature of from about 400° to 900° C. such that an activepolymerization catalyst is formed, and (d) contacting the monomer withthe active polymerization catalyst in the presence of an aluminumtrialkyl, said tetravelent titanium compound being added in an amountsufficient to give a titanium concentration in the range of 0.05 to 20%by weight and said aluminum trialkyl being employed in the amount of 0.1to 100% by weight based on the total weight of the catalyst.
 2. Aprocess as claimed in claim 1 wherein ethylene is the sole 1-olefinicmonomer.
 3. A process as claimed in claim 1 wherein the titaniumcompound has the general formula (RO)₄ Ti wherein R represents an alkylgroup containing 1 to 6 carbon atoms.
 4. A process as claimed in claim 1wherein the titanium compound is tetraethyl titanate or tetraisopropyltitanate.
 5. A process as claimed in claim 1 wherein the quantity oftitanium compound employed is sufficient to give a titaniumconcentration in the product from step (b) in the range 0.5 to 5 wt %.6. A process as claimed in claim 1 wherein the organometallic compoundis triethyl aluminium or triisobutyl aluminium.
 7. A process as claimedin claim 1 wherein the polymerisation is carried out by contacting themonomer with a suspension or a fluidised bed of the catalyst particlesin a fluid medium under conditions such that the polymeric 1-olefinforms as solid particles suspended in or fluidised in the fluid medium.8. A process as defined in claim 1, wherein the quantity of chromiumcompound supported on the refractory oxide is sufficient to provide achromium concentration of about 0.2 to 30 wt. % based on the weight ofthe chromium compound and support together.
 9. A catalyst forpolymerizing 1-olefine prepared by (a) supporting chromium oxide, or acompound calcinable thereto at a heating temperature stated in part (c)hereof, on a refractory oxide support material comprising silica, (b)adding a tetravalent titanium compound having the general formulaTi(OR)_(m) X_(n), wherein m+n is 4, m is zero or an integer from 1 to 4,R is an organic hydrocarbon group having 1 to 12 carbon atoms, X ishalogen or a hydrocarbon group and when the titanium compound containsmore than one R or X group the groups may be the same or different, (c)heating the product at a temperature of from about 400° to 900° C. suchthat an active polymerization catalyst is formed and (d) adding to theactive polymerization catalyst an aluminum trialkyl compound, saidtetravalent titanium compound being added in an amount sufficient togive a titanium concentration in the range of 0.05 to 20% by weight andsaid aluminum trialkyl being employed in an amount of 0.01 to 100% byweight based on the total weight of the catalyst.
 10. A catalyst forpolymerizing 1-olefins as defined in claim 9, wherein the quantity ofchrominum compound supported on the refractory oxide is sufficient toprovide a chrominum concentration of about 0.2 to 30 wt. % based on theweight of the chromium compound and support together.